io_uring: unlock sqd->lock before sq thread release CPU

The sq thread actively releases CPU resources by calling the
cond_resched() and schedule() interfaces when it is idle. Therefore,
more resources are available for other threads to run.

There exists a problem in sq thread: it does not unlock sqd->lock before
releasing CPU resources every time. This makes other threads pending on
sqd->lock for a long time. For example, the following interfaces all
require sqd->lock: io_sq_offload_create(), io_register_iowq_max_workers()
and io_ring_exit_work().

Before the sq thread releases CPU resources, unlocking sqd->lock will
provide the user a better experience because it can respond quickly to
user requests.

Signed-off-by: Kanchan Joshi<joshi.k@samsung.com>
Signed-off-by: Wenwen Chen<wenwen.chen@samsung.com>
Link: https://lore.kernel.org/r/20230525082626.577862-1-wenwen.chen@samsung.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/sqpoll.c b/io_uring/sqpoll.c
index 9db4bc1f521a3162d3480000cdc82e9a1aacfe62..5e329e3cd4706196fb6ce643ce35fbf9ad097360 100644 (file)
--- a/io_uring/sqpoll.c
+++ b/io_uring/sqpoll.c
@@ -255,9 +255,13 @@ static int io_sq_thread(void *data)
                        sqt_spin = true;
 
                if (sqt_spin || !time_after(jiffies, timeout)) {
-                       cond_resched();
                        if (sqt_spin)
                                timeout = jiffies + sqd->sq_thread_idle;
+                       if (unlikely(need_resched())) {
+                               mutex_unlock(&sqd->lock);
+                               cond_resched();
+                               mutex_lock(&sqd->lock);
+                       }
                        continue;
                }